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  <h1 class="topictitle1">Backup and Restoration of Large-Capacity VM Disks in NBD/NBDSSL Transmission Mode Fail</h1>
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    <h4 class="sectiontitle">Symptom</h4>
    <p>Backup or restoration of large-capacity (TB-level) VM disks in NBD/NBDSSL transmission mode fails, with an error message displayed, indicating that the client fails to back up or restore disks.</p>
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    <h4 class="sectiontitle">Possible Causes</h4>
    <p>In NBD/NBDSSL transmission mode, the network is used to transmit data. If the entire network transmission link times out or fluctuates, the read and write operations on production disks through the Virtual Disk Development Kit (VDDK) will fail, and backup or restoration cannot be retried in a short period of time.</p>
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    <h4 class="sectiontitle">Troubleshooting</h4>
    <p>In NBD/NBDSSL transmission mode, the management network bandwidth is occupied and the transmission rate is low. Therefore, you are advised to use the SAN or hot-add transmission mode to back up and restore large-capacity (TB-level) disks.</p>
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     <strong>Parent topic:</strong> <a href="en-us_topic_0000002200054965.html">FAQs</a>
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